The gluonic contributions are not considered in our
calculation, because it is shown that (1) the fraction
of gluonium contributions to \({\eta }\)  and \({\eta }^{\prime }\) 
is less than 15% [1]};
(2) the flavor-singlet contributions from the gluonic content
of \({\eta }^{({\prime })}\)  meson is very small and can be
neglected safely [2]}.
In addition, the contributions from the possible \(c\bar{c}\) 
compositions of \({\eta }^{({\prime })}\)  meson is also not
considered here.
